The use of graphics in computer applications is very widespread. The transmission of a document between computers often includes the transmission of graphical data such as character fonts. This includes the transmission of facsimile messages from one facsimile (FAX) machine to another FAX machine, or the transmission of data from a host computer to a printer.
Graphical data may be transmitted as raster graphics data in which the graphic image is rendered into a bit-map data file prior to transmission. For example, a FAX machine scans a document and generates a bit-map data file for each page. The bit-map data file is compressed prior to transmission to reduce the transmission time. This compression permits greater computing efficiency and also saves money if the facsimile telephone call is a long distance call. There are a number of well known facsimile compression standards that are defined by standards established by The International Telegraph and Telephone Consultative Committee (CCITT). Despite their widespread use, data compression using the CCITT compression standards is slow and does not result in efficient compression of a graphic image.
Computers, such as those that are part of a printer coupled to a host computer, may transfer image data relating to the pages to be printed by the printer. Often the printer receives character fonts embedded within text data. The printer can use the embedded character font to print high quality output in the desired font. A common element in all of these examples is that one computer sends an image to a second computer.
The resources required to transfer the image data vary from system to system. For example, some word processing systems, such as the Microsoft Word.TM. word processor, require a powerful central processing unit (CPU) with sophisticated computing capability and large amounts of memory to process the image data. Similarly, printing systems such as those using the PostScript.TM. software, require a great deal of data processing by both the transmitting computer and the receiving computer. Again, this requires both a powerful CPU and large amounts of memory.
The types of image transmission systems described above may not be appropriate for use in low-cost systems where the cost of a powerful CPU and large amounts of memory is not acceptable. Therefore, it can be appreciated that there is a great need for a system and method for compressing raster graphic images and transferring image data without requiring a powerful CPU and large amounts of memory.